The present invention relates to a light-source device capable of illuminating the desired area to be illuminated with high illuminance and further capable of achieving high uniformity of illuminance.
The present invention also relates to a projection-type display device incorporating the light-source device and, more precisely, to a projection-type display device the projected picture image from which is of high brightness and low in the nonuniformity of brightness.
FIG. 27 is a structural drawing showing the general structure of the optical system of a projection-type display device 40 and a light-source device 10 according to prior art.
As is shown in the drawing, conventional light-source device 10 comprises a lamp 21, an elliptical mirror 22 of which the reflecting surface is an elliptical surface that is rotationally symmetrical with respect to optical axis AX, and a condenser lens 23. Lamp 21 is so disposed that its center of emission is located in the vicinity of a first focal point FP.sub.1 of the elliptical mirror 22. Thus light L.sub.1 emitted by the lamp 21 and reflected by the elliptical mirror 22 is condensed at a convergence point CP in the vicinity of a second focal point FP.sub.2 of the elliptical mirror 22, forming an image of the lamp 21. Further, the condenser lens 23 is so disposed that the position of the focal point on its front side (considering, here and hereafter in these specifications, the lamp 21 side as the front, or forward, side and the screen SC side as the rear, or rearward, side) coincides with the convergence point CP. Thus light L.sub.1 passing through the convergence point CP and impinging on the condenser lens 23 becomes a parallel luminous flux L.sub.2 illuminating the surface to be illuminated (in this case liquid crystal panel 61).
Conventional projection-type display device 40 further comprises, in addition to the light-source device 10, a liquid crystal panel 61 that functions as a light valve, and a projector lens 62. Note that, in the drawing, SC designates the screen on which the picture image is projected.
The liquid crystal panel 61 comprises an image display area for the display of a picture image based on electrical signals from a driver circuit (not shown), the optical transmittance of which varies in accordance with the density and color of the picture image displayed. The luminous flux L.sub.3 that has passed through the liquid crystal panel 61 then passes through the projector lens 62, becomes projected light L.sub.4, and is projected onto the screen SC.
FIG. 28 is a structural drawing showing the general structure of the optical system of a projection-type display device 41 capable of magnifying and displaying a color picture image according to prior art.
The projection-type display device 41 comprises, in addition to the light-source device 10 of the same structure as shown in FIG. 27, a dichroic mirror 63R for color separation that reflects only red light L.sub.r and transmits other color components, a dichroic mirror 63B for color separation that reflects only blue light L.sub.b and transmits other color components, and light-reflecting mirrors 64R and 64G. Further, the projection-type display device 41 comprises a dichroic mirror 66B for color synthesis that reflects only blue light L.sub.b and transmits other color components, a dichroic mirror 66G for color synthesis that reflects only green light L.sub.g and transmits other color components, liquid crystal panels 61R, 61G, and 61B, field lenses 65R, 65G and 65B, and a projector lens 62.
In the projection-type display device 41, the red component L.sub.r of luminous flux L.sub.2 emitted from the light-source device 10 is reflected by the dichroic mirror 63R, its direction is changed by the mirror 64R, passes through the liquid crystal panel 61R and the field lens 65R, and then passes through the dichroic mirrors 66B and 66G and impinges on the projector lens 62. The blue component L.sub.b passes through the dichroic mirror 63R, is reflected by the dichroic mirror 63B, passes through the liquid crystal panel 61B and the field lens 65B, is reflected by the dichroic mirror 66B, passes through the dichroic mirror 66G and impinges oil the projector lens 62. The green component L.sub.g passes through the dichroic mirrors 63R and (63B, passes through the liquid crystal panel 61G and the field lens 65G, its direction is changed by the mirror 64G, is reflected by the dichroic mirror 66G, and impinges on the projector lens 62.
Nevertheless, a problem arises in that, while the cross-sectional configuration of luminous flux L.sub.2 emitted by the light-source device 10 above described is circular, the image display area of the liquid crystal panel 61 is generally rectangular, so that, as shown in FIG. 29, it is necessary for the diameter of luminous flux L.sub.2 to be greater than the diagonal dimension of rectangular image display area 70, with the result that, since the light impinging on the cross-hatched portion is wasted, the luminous energy passing through the image display area 70 and impinging on the projector lens 62 is reduced and it becomes difficult to increase the brightness of the projected image.
A further problem arises in that, since the luminous intensity of the lamp 21 generally varies in accordance with the direction of emission, luminous flux L.sub.2 emitted from the light-source device 10 is not uniform, giving rise to nonuniformities in the brightness of the projected image. As shown, for example, in FIG. 27 and FIG. 28, when the lamp 21 is a discharge lamp having its discharge electrode disposed parallel to optical axis AX, the luminous intensity in the direction of optical axis AX is small, with the result that the brightness near the center of the projected image is low.